Why did my check engine light come on after getting gas?

9 times out of 10 a CEL that triggers within a day of refueling is a loose gas cap — the EVAP system runs a leak test and a cap that wasn't clicked tight fails it. Tighten the cap until it clicks 3 times. The light may take 1–2 drive cycles to clear on its own. If it doesn't clear in a week, the cap's gasket may be cracked ($15 part) or there's a bigger EVAP leak.

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